/*
 * Copyright (C) 2012 The Guava Authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.google.common.collect;

import static com.google.common.base.Preconditions.checkNotNull;

import com.google.common.annotations.GwtCompatible;
import com.google.errorprone.annotations.CanIgnoreReturnValue;
import com.google.errorprone.annotations.concurrent.LazyInit;
import com.google.j2objc.annotations.WeakOuter;

import java.util.AbstractCollection;
import java.util.Collection;
import java.util.Iterator;
import java.util.Map;
import java.util.Map.Entry;
import java.util.Set;
import java.util.Spliterator;
import java.util.Spliterators;
import javax.annotation.CheckForNull;

import org.checkerframework.checker.nullness.qual.Nullable;

/**
 * A skeleton {@code Multimap} implementation, not necessarily in terms of a {@code Map}.
 *
 * @author Louis Wasserman
 */
@GwtCompatible
@ElementTypesAreNonnullByDefault
abstract class AbstractMultimap<K extends @Nullable Object, V extends @Nullable Object>
        implements Multimap<K, V>
{
    @Override
    public boolean isEmpty()
    {
        return size() == 0;
    }

    @Override
    public boolean containsValue(@CheckForNull Object value)
    {
        for (Collection<V> collection : asMap().values())
        {
            if (collection.contains(value))
            {
                return true;
            }
        }

        return false;
    }

    @Override
    public boolean containsEntry(@CheckForNull Object key, @CheckForNull Object value)
    {
        Collection<V> collection = asMap().get(key);
        return collection != null && collection.contains(value);
    }

    @CanIgnoreReturnValue
    @Override
    public boolean remove(@CheckForNull Object key, @CheckForNull Object value)
    {
        Collection<V> collection = asMap().get(key);
        return collection != null && collection.remove(value);
    }

    @CanIgnoreReturnValue
    @Override
    public boolean put(@ParametricNullness K key, @ParametricNullness V value)
    {
        return get(key).add(value);
    }

    @CanIgnoreReturnValue
    @Override
    public boolean putAll(@ParametricNullness K key, Iterable<? extends V> values)
    {
        checkNotNull(values);
        // make sure we only call values.iterator() once
        // and we only call get(key) if values is nonempty
        if (values instanceof Collection)
        {
            Collection<? extends V> valueCollection = (Collection<? extends V>) values;
            return !valueCollection.isEmpty() && get(key).addAll(valueCollection);
        }
        else
        {
            Iterator<? extends V> valueItr = values.iterator();
            return valueItr.hasNext() && Iterators.addAll(get(key), valueItr);
        }
    }

    @CanIgnoreReturnValue
    @Override
    public boolean putAll(Multimap<? extends K, ? extends V> multimap)
    {
        boolean changed = false;
        for (Entry<? extends K, ? extends V> entry : multimap.entries())
        {
            changed |= put(entry.getKey(), entry.getValue());
        }
        return changed;
    }

    @CanIgnoreReturnValue
    @Override
    public Collection<V> replaceValues(@ParametricNullness K key, Iterable<? extends V> values)
    {
        checkNotNull(values);
        Collection<V> result = removeAll(key);
        putAll(key, values);
        return result;
    }

    @LazyInit
    @CheckForNull
    private transient Collection<Entry<K, V>> entries;

    @Override
    public Collection<Entry<K, V>> entries()
    {
        Collection<Entry<K, V>> result = entries;
        return (result == null) ? entries = createEntries() : result;
    }

    abstract Collection<Entry<K, V>> createEntries();

    @WeakOuter
    class Entries extends Multimaps.Entries<K, V>
    {
        @Override
        Multimap<K, V> multimap()
        {
            return AbstractMultimap.this;
        }

        @Override
        public Iterator<Entry<K, V>> iterator()
        {
            return entryIterator();
        }

        @Override
        public Spliterator<Entry<K, V>> spliterator()
        {
            return entrySpliterator();
        }
    }

    @WeakOuter
    class EntrySet extends Entries implements Set<Entry<K, V>>
    {
        @Override
        public int hashCode()
        {
            return Sets.hashCodeImpl(this);
        }

        @Override
        public boolean equals(@CheckForNull Object obj)
        {
            return Sets.equalsImpl(this, obj);
        }
    }

    abstract Iterator<Entry<K, V>> entryIterator();

    Spliterator<Entry<K, V>> entrySpliterator()
    {
        return Spliterators.spliterator(
                entryIterator(), size(), (this instanceof SetMultimap) ? Spliterator.DISTINCT : 0);
    }

    @LazyInit
    @CheckForNull
    private transient Set<K> keySet;

    @Override
    public Set<K> keySet()
    {
        Set<K> result = keySet;
        return (result == null) ? keySet = createKeySet() : result;
    }

    abstract Set<K> createKeySet();

    @LazyInit
    @CheckForNull
    private transient Multiset<K> keys;

    @Override
    public Multiset<K> keys()
    {
        Multiset<K> result = keys;
        return (result == null) ? keys = createKeys() : result;
    }

    abstract Multiset<K> createKeys();

    @LazyInit
    @CheckForNull
    private transient Collection<V> values;

    @Override
    public Collection<V> values()
    {
        Collection<V> result = values;
        return (result == null) ? values = createValues() : result;
    }

    abstract Collection<V> createValues();

    @WeakOuter
    class Values extends AbstractCollection<V>
    {
        @Override
        public Iterator<V> iterator()
        {
            return valueIterator();
        }

        @Override
        public Spliterator<V> spliterator()
        {
            return valueSpliterator();
        }

        @Override
        public int size()
        {
            return AbstractMultimap.this.size();
        }

        @Override
        public boolean contains(@CheckForNull Object o)
        {
            return AbstractMultimap.this.containsValue(o);
        }

        @Override
        public void clear()
        {
            AbstractMultimap.this.clear();
        }
    }

    Iterator<V> valueIterator()
    {
        return Maps.valueIterator(entries().iterator());
    }

    Spliterator<V> valueSpliterator()
    {
        return Spliterators.spliterator(valueIterator(), size(), 0);
    }

    @LazyInit
    @CheckForNull
    private transient Map<K, Collection<V>> asMap;

    @Override
    public Map<K, Collection<V>> asMap()
    {
        Map<K, Collection<V>> result = asMap;
        return (result == null) ? asMap = createAsMap() : result;
    }

    abstract Map<K, Collection<V>> createAsMap();

    // Comparison and hashing

    @Override
    public boolean equals(@CheckForNull Object object)
    {
        return Multimaps.equalsImpl(this, object);
    }

    /**
     * Returns the hash code for this multimap.
     *
     * <p>The hash code of a multimap is defined as the hash code of the map view, as returned by
     * {@link Multimap#asMap}.
     *
     * @see Map#hashCode
     */
    @Override
    public int hashCode()
    {
        return asMap().hashCode();
    }

    /**
     * Returns a string representation of the multimap, generated by calling {@code toString} on the
     * map returned by {@link Multimap#asMap}.
     *
     * @return a string representation of the multimap
     */
    @Override
    public String toString()
    {
        return asMap().toString();
    }
}
